The present invention relates to a nitrogen fertilizer having a long-term action based on urea-formaldehyde condensation products suspended in water, and to a process for its manufacture.
Customary nitrogen fertilizers based on ammonium or nitrate salts and urea have the disadvantage that they are rapidly consumed in the soil and are thus available to the plants for only a short time, with the result that frequent fertilization is necessary during the vegetation period.
This short duration of action of the nitrogen fertilizers can be attributed to many causes. Since the soil cannot retain the nitrate ion, the nitrogen in nitrate form is very easily washed out into the lower layers of soil and can no longer be reached by the roots of the plants. The ammonium ion is well fixed in the soil, but nitrifying bacteria such as Nitrosomonas and Nitrobacter very quickly convert it into the nitrate form. Urea is also converted in the soil, first, by urease, into ammonium nitrogen, and then the latter is converted back into a nitrate by means of nitrification. The nitrate can, as stated above, be washed out very easily and thus under certain circumstances leads to problems in the production of drinking water.
The disadvantage that too little nitrogen is supplied to the plants cannot even be avoided by, for example, a high dose of fertilizer, because an excessive nitrate content in plants can also be detrimental to health.
In order to avoid these disadvantages an attempt has been made to manufacture nitrogen fertilizers that are more stable and have a slower action. For example, urea-formaldehyde condensation products, so-called "urea-forms", are sparingly soluble in water and are degraded slowly in damp soil by microbial decomposition and are thus available to the plants as a source of nitrogen over a longer period of time.
A disadvantage of these urea-formaldehyde condensation products is that, when they are used in the form of dispersions, they thicken or crystallize and lose their flowability and can no longer be applied by means of the customary spraying apparatus.
U.S. Pat. Nos. 4,298,512 and 4,332,610 propose the use of relatively large amounts of aldehydes, such as acetaldehyde, propionaldehyde or butyraldehyde, in order to stabilize the urea-formaldehyde dispersions. As a result of this measure, however, the nitrogen content of these fertilizers is considerably reduced and the price becomes uneconomically high, due to the relatively expensive additives.
Therefore, a principal object of the present invention was to develop a nitrogen fertilizer having a long-term action based on urea-formaldehyde condensation products suspended in water, which does not have the mentioned disadvantages, has adequate stability and a high nitrogen content, and does not require expensive additives.